1. Field of the Invention
The present invention generally relates to a music sound correcting apparatus and a music sound correcting method for correcting music sounds. More specifically, the present invention is directed to a technique capable of correcting music sounds in such a manner that even when music sounds of electronic musical equipments are reproduced by using a speaker, or a headphone, similar audibilities can be established.
2. Description of the Related Art
In general, music sounds produced from electronic musical instruments such as electronic pianos and electronic keyboards can be heard through speakers, or headphones. Referring now to drawings, a conventional electronic musical instrument will be described.
FIG. 1 is a schematic block diagram for mainly indicating a signal output system of one typical conventional electronic musical instrument. This electronic musical instrument is mainly arranged by a central processing unit (will be referred to as a "CPU" hereinafter) 50, a keyboard 51, a sound source 52, a preamplifier 53, a sound volume controller 54, a main amplifier 55, a switch 56, a speaker 57, a headphone amplifier 58, and also a headphone jack 59. A plug 61 of the headphone 60 is inserted into the headphone jack 59. The switch 56 is turned OFF when the plug 61 of the headphone 60 is inserted into the headphone jack 59, whereas this switch 56 is turned ON when this plug 61 is pulled out from the headphone jack 59.
The keyboard data produced by operating the keyboard 51 is supplied to the CPU 50. The CPU 50 produces the music sound data based on this keyboard data, and then supplies this music sound data to the sound source 52. The sound source 52 produces the analog music sound signal based on this music sound data, and then supplies this analog music sound signal to the preamplifier 53. The preamplifier 53 amplifies the analog music sound signal supplied from the sound source 52 by an amplification factor defined based upon the sound volume control signal derived from the sound volume controller 54. Then, the amplified analog music sound signal is supplied to the main amplifier 55 and the headphone amplifier 58.
The main amplifier 55 amplifies the analog music sound signal amplified by the preamplifier 53 so as to produce such a signal having a sufficiently large amplitude capable of driving the speaker 57, and then supplies this amplified music sound signal to the switch 56. When the plug 61 of the headphone 60 is not inserted into the headphone jack 59, this amplified music sound signal derived from the main amplifier 55 is supplied via this switch 56 to the speaker 57. As a result, the music sound can be reproduced from the speaker 57.
On the other hand, the headphone amplifier 58 amplifies the analog music sound signal amplified by the preamplifier 53 so as to produce such a signal having a sufficiently large amplitude capable of driving the headphone 60, and then supplies this amplified music sound signal to the headphone jack 59. When the plug 61 of the headphone 60 is inserted into the headphone jack 59, this amplified music sound signal derived from the headphone amplifier 58 is supplied via this headphone jack 59 and the plug 61 to the headphone 60. As a result, the music sound can be reproduced from the headphone 60. In this case, since the switch 56 is turned OFF, no music sound is reproduced from the speaker 57.
The conventional electronic musical instrument with the above arrangement owns the following problem. That is, when one music sound (music sound source) is reproduced, the audience has different audibilities when the music sound is reproduced from the speaker, and also when this music sound is reproduced from the headphone. This problem may be caused by the differences existed in the frequency characteristics, the sound image localizing mechanism, and the reverberation characteristics while the same music sound is reproduced by employing the speaker and the headphone. Now, these factors will be explained as follows:
(1). Frequency characteristic
In general, a frequency characteristic of a speaker is considerably deteriorated, as compared with a frequency characteristic of a headphone. Also, the frequency characteristic of the medium and low sound ranges is greatly influenced by enclosures. Furthermore, in an electronic musical instrument, a speaker is not always located at an ideal speaker setting position with respect to an audience, which is completely different from a so-called "audio apparatus". As a result, the frequency characteristic is also adversely influenced by the directivity of the speaker.
As a consequence, in order to improve the frequency characteristic when the music sound is reproduced by using the speaker in the conventional electronic musical instrument, as illustrated in FIG. 2, an equalizer circuit 70 is provided between the preamplifier 53 and the main amplifier 55. This equalizer circuit 70 controls the gains of the plural frequency ranges. As a result, the frequency characteristic obtained during the speaker reproducing operation can be improved. For instance, as shown in FIG. 3, as this equalizer circuit 70, the gains of the three frequency ranges can be independently controlled. It should be noted that since the arrangement and the operation of this equalizer circuit 70 are well known in the field, a detailed description thereof is omitted.
(2). Sound image localization
The frequency characteristic obtained while the music sound is reproduced by employing the headphone is not so deteriorated, as compared with the above-explained speaker reproducing operation. However, there is such a trend that the sound images are concentrated around the head of the audience to be localized. This is caused by the following reason. That is, as indicated in FIG. 4, when the audience hears the sounds reproduced from the speaker, the sound reproduced from the left speaker SPL in response to the left-channel signal reaches the left ear of the audience and further reaches the right ear of this audience. Similarly, the sound reproduced from the right speaker in response to the right channel signal reaches the right ear of the audience and also reaches the left ear of this audience.
In this case, both the sound which reaches from the left speaker SPL to the left ear of the audience, and the sound which reaches from the right speaker SPR to the right ear of this audience are referred to as "direct sounds" (indicated by solid lines). Also, both the sound which reaches from the left speaker SPL to the right ear of the audience, and the sound which reaches from the right speaker SPR to the left ear of this audience are referred to as "crosstalk sounds" (indicated by broken lines).
On the other hand, when the audience hears the music sound reproduced by using the headphone, the sound reproduced in response to the left-channel signal reaches only the left ear of this audience, and the sound reproduced in response to the right-channel signal reaches only the right ear of this audience. In other words, only the direct sounds are entered to the ears of the audience, and no crosstalk sounds are entered. This phenomenon may cause that the sound images are concentrated around the head of this audience to be localized. In this case, when the audience uses the headphone long time, there is a problem that this audience has weary feelings.
Also, different from the above-explained speaker reproducing operation, when the audience hears the sounds reproduced by using the headphone, this audience is not completely adversely influenced by the directivity of the speaker at the listening point. As a consequence, the audience may have a sense of incongruity, since such a sound which can be hardly heard by the audience during the speaker reproducing operation may be heard during the headphone reproducing operation, and conversely, such a sound which can be surely heard by the audience during the speaker reproducing operation may not be heard during the headphone reproducing operation.
To solve these problems, when the music sound is reproduced by the headphone, the two techniques have been developed, namely the first technique capable of adding the crosstalk sound to the direct sound so as to localize the sound image, and the second technique capable of employing the external-ear transfer function so as to localize the sound image.
In accordance with the first localizing technique, for example, such a circuit as shown in FIG. 5 may be used. That is, the signal produced by delaying the left-channel input signal Lin by the delay device 80a is added to the right-channel input signal Rin by the adder 81b so as to produce the right-channel output signal Rout. Similarly, the signal produced by delaying the right-channel input signal Rin by the delay device 80b is added to the left-channel input signal Lin by the adder 81a so as to produce the left-channel output signal Lout. The delay amount of each of the delay devices 80a and 80b is equal to a difference between time during which a direct sound reaches one ear, and time during which a crosstalk sound reaches this ear (will be referred to as an "inter aural time difference" hereinafter), for instance, is on the order of 0.2 ms.
In accordance with the second localizing technique, for example, such a circuit as indicated in FIG. 6 may be used. This circuit is arranged by the filters 90a and 90b for simulating the external-ear transfer function of the direct sound; the filters 91a and 91b for simulating the external-ear transfer function of the crosstalk sound; the delay devices 92a and 92b for simulating the inter aural time differences; and also the adders 93a and 93b. In this circuit, the adder 93a adds the signal produced by filtering the left-channel input signal Lin by the filter 90a to another signal which is produced by filtering the right-channel input signal Rin by the filter 91b and further by delaying this filtered input signal by the delay device 92b so as to produce the left-channel output signal Lout. Similarly, the adder 93b adds the signal produced by filtering the right-channel input signal Rin by the filter 90b to another signal which is produced by filtering the left-channel input signal Lin by the filter 91a and further by delaying this filtered input signal by the delay device 92a so as to produce the right-channel output signal Lout. When the audience hears such sounds produced in response to the left-channel output signal Lout and the right-channel output signal Rout, which are produced by employing the first and second localizing techniques, the audience can feel that the sound image is clearly localized.
(3). Reverberation characteristics
As previously described, when the audience hears the music sounds reproduced from the headphone, only the direct sound is entered into the ears of this audience. In other words, all of the reverberation sounds occurred in the listening room when the audience hears the music sound reproduced from the speaker are cut. As a consequence, there is such a problem that when the audience hears the music sounds reproduced from the headphone, the audience cannot have the stereophonic feelings, but also a lack of front localization of the sound image.
As previously explained, in the conventional electronic musical instrument, when trying to obtain the preferable music sound reproduced from both the speaker reproducing operation and the headphone reproducing operation, the above-described various characteristics such as the frequency characteristic, the sound image localizing mechanism, and the reverberation characteristic must be necessarily improved. For this porpoise, the following various circuits are required, namely, the equalizer circuit capable of improving the frequency characteristic; the delay device/adder capable of clearly localizing the sound image; the filter/delay device/adder capable of simulating the external-ear transfer function; and the circuit capable of simulating the reverberation characteristic. However, if all of these circuits for improving characteristics are equipped with the conventional electronic musical instrument, the entire circuit scale is increased and the higher cost is required. Moreover, there is a useless characteristic improving circuit, because the speaker reproducing operation and the headphone reproducing operation are not carried out at the same time.